Fix compatibility with region inference

[chm10]

Tested with us-east-1 and will solve issue with EU regions too for Claude Sonnet 3.5.

*Issue #508 and #527

Description of changes:
Get the region from BEDROCK_REGION and adapt to cross reference region format.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[statefb]

@chm10 Hi, thank you so much for creating PR! LGTM except for CI failure (mypy check). Could you create a commit to fix it? (Need to add two spaces before comment)

region = BEDROCK_REGION.split("-")[0] # Cross-region inference

[statefb]

close #508
close #527

[statefb]

LGTM!

[statefb]

@chm10 Sorry, we need to consider following things. Could you re-create a PR including following modification?

• Only limited regions supports inference profile (currently us and eu only)
  • we can check if the region supports by aws bedrock list-inference-profiles --profile <profile-name>
• Due to the architecture to routing requests, latency happens (see doc). Could you add enableBedrockCrossRegionInference option to cdk.json with the default value false?
  • Even the value is set to true, if the bedrockRegion is not included in the supported region, model id without cross region inference should be chosen. Also warning log should be added.

Thank you in advance!